Square loop magnetic manganeseferrite material and manufacture thereof



Sept. 18, 1962 E. c. LEAYCRAFT 3,054,752

SQUARE LOOP MAGNETIC MANGANESE-FERRITE MATERIAL. AND MANUFACTURE THEREOF Filed Nov. 10, 1959 6 Sheets-Sheet 1 emcee-ww SINTERING ALL S.YMBOLS PRESSED 1200 DENSITY\ CALCINE 950 PARTICLE 700 SIZE INVENTOR COERCIVITY IN OERSTEDS EDGAR c. LEAYCRAH 11%..ERRAERMRA ATTORNEY Sept. 18, 1962 Filed Nov. 10, 1959 r VI wVO

6 Sheets-Sheet 2 FIG.2

Fe O AVERAGE PARTICLE SIZE IN MICRONS Sept. 18, 1962 E. c. LEAYCRAFT 3,054,752

SQUARE LOOP MAGNETIC MANGANESE-FERRITE MATERIAL AND MANUFACTURE THEREOF Filed Nov. 10, 1959 6 Sheets-Sheet 3 FIG.3

CALCINE TEMPERATURE IN O C Sept. 18, 1962 E. c. LEAYCRAFT 3,054,752

SQUARE LOOP MAGNETIC MANGANESE-FERRITE MATERIAL. AND MANUFACTURE THEREOF Filed Nov. 10, 1959 6 Sheets-Sheet 4 '2.50 2,60 2.70 2.80 2.90 3.60 3.10 3.20 3.30 3.40 3.50 PRESSED DENSITY IN GRAMS/CC Hex 10\ 3 B 16 FIG.7

p 1962 E. c. LEAYCRAFT 3,054,752

SQUARE LOOP MAGNETIC MANGANESE-FERRITE MATERIAL AND MANUFACTURE THEREOF Filed Nov. 10, 1959 6 Sheets-Sheet F I G 5 NCM AC=L8 107 K-10Y 106 r V1 Ho =3 4 w V0 "0 L 108 109 3'5 K-IOY 1H 0 SINTERING TEMPERATURE IN DEGREES CENTIGRADE Sept. 18, 1962 Filed NOV. 10, 1959 wVo E. C. LEAYCRAFT SQUARE LOOP MAGNETIC MANGANESE-FERRITE MATERIAL AND MANUFACTURE THEREOF 6 Sheets-Sheet 6 NCM 2 Hem 125 K 1 SINTERED DENSITY IN GRAMS/CC United States Patent 3,054,752 SQUARE LOOP MAGNETIC MANGANESE- FE MATERIAL AND MANUFACTURE THEREOF Edgar C. Leaycratt, Woodstock, N.Y., assignor to International Business Machines Corporation, New York,

N.Y., a corporation of New York Filed Nov. 10, 1959, Ser. No. 851,997 9 Claims. (Cl. 25262.5)

This invention relates to square hysteresis characteristic magnetic manganese-ferrite materials and more particularly to materials of this type employed in the manufaeture of magnetic core elements providing bi-stable binary memory elements, and to the process of manufacture thereof.

In electrical computer apparatus, the bi-stable square loop magnetic core element has become a well known and valuable piece of apparatus. The use and function of this element has been variously described in numerous patents, one of which is the patent to Greenhalgh 2,872,666, issued February 3, 1959. This and numerous other patents refer to the square hysteresis loop characteristic of cores making it possible to employ the core in coincident current switching operations in which the existence of a half select current in a conductor will not drive the core to the knee of the hysteresis loop and thus will not switch the core but the coincident existence of a second half select current of equal magnitude to the first half select current will drive the core to saturation and cause the magnetic state of the core to switch, whereupon, after the driving forces are relieved, the core will retain to a high degree the new magnetic state. In operations such as this, it is essential that a core of maximum squareness be provided.

It is accordingly a primary object of this invention to provide manganese-ferrite cores of maximum squareness over a range of coercivities.

It has long been known that cores of various coercivities can be produced by varying core compositions and sintering temperatures. However, I have found that cores of maximum squareness can be produced from manganeseferrite systems with or Without small percentages of additives and over a range of coercivities if not only sintering temperatures but also iron oxide powder particle size, calcining temperatures and pressed densities are selected in order to produce in a finished core a sintered density of optimum value.

I have found that manganese-ferrite cores of various coercivities have optimum squareness when their sintered densities are approximately 4.49 to 4.53 grams per cubic centimeter, the good squareness results within the range of approximately 4.48 to 4.55. It is the object of this invention to set forth the limits of the process variables noted above within which optimum squareness and the desired sintered density are produced in manganese-ferrite core systems within a limited range of coercivities.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a plot showing, for manganese-ferrite systems, values of the process variables for the production of maximum squareness cores having various sintered density.

. FIGURE 2 is a plot, for manganese-ferrite system of FIGURE 1, of iron oxide particle size versus squareness.

FIGURE. 3 is a plot, for manganese-ferrite systems of FIGURE 1, of calcining temperature versus squareness.

FIGURE 4 is a plot, for manganese-ferrite systems of 3,054,752 Patented Sept. 18, 1962 2 FIGURE 1, of pressed density versus squareness; and

FIGURE 5 is a plot, for manganese-ferrite systems of FIGURE 1, of sintering temperature versus squareness.

FIGURE 6 is a plot, for manganese-ferrite systems of FIGURE 1, of sintered density versus squareness.

FIGURE 7 is a showing of a hysteresis loop and indicates diagrammatically full and half select pulses for switching and resulting output voltages.

As has been previously noted, ferromagnetic bodies employed as magnetic memory elements are desirably possessed of a square hysteresis characteristic. In FIG- URE 7, there is indicated generally at 10, a hysteresis loop of such a body. The loop is drawn on conventional B and H coordinates. If there is applied to the body a full select "1 driving force on the H axis as indicated by the pulse 12, the body will be driven to a H-B state or a "1 state as indicated by the point 14 on the loop, and, when the driving force is relieved, the residual magnetism in the core Br will be at a value indicated by the point 16 on the B axis. Similarly, if a full selected 0 drive pulse 18 is applied to the body, the magnetic state of the body will be switched to a (--)B state or the 0 state as indicated by the point 20 on the loop, and, when the driving force is relieved, the body will retain a residual magnetism indicated by the point 22 on the B axis.

If, while the body represented by the loop has a residual magnetism of value indicated by the point '16, a half select 0 pulse as indicated at 24 is applied thereto and then relieved, the degree of magnetism thereafter remaining in the body may, for example, be indicated by the point 26. Similarly, if when the body is at a magnetic state indicated by the point 22 a half select 1 pulse 28 is applied thereto and relieved, the magnetic state of the body remaining thereafter may, for example, be indicated by the point 30. It should be noted that the actual points shown on the diagram are displacements which are selected for the purpose of clarity and are not intended to be indicative dimensionally of any exact condition prevailing for any given body.

When the body is at a magnetic state as indicated by the point 16, the application of a full select 0 pulse 18 will produce an output voltage indicated by the dimension V If the same full select 0 pulse is applied when the body had a residual state as indicated by the point 2.6-, a lesser output voltage will be generated. This voltage is indicated at V Similarly, if the magnetic body had a residual state as indicated by the point 22 and a full select 0 pulse 18 were applied, an output voltage V would be generated, and if the magnetic state had been at the point indicated at '30, upon an application of a full select 0 pulse, an output would have occurred as indicated at V It will be evident that the degree of squareness is indicated by the displacement between points 22 and 30, and by the displacement between points 26 and 16.

Thus, the ratio V V provides a highly satisfactory measure of squareness in that V is a relatively absolute value of disturbance resulting from lack of perfect squareness and V accommodates for the fact that various materials will have hysteresis loops of various B/H ratios. Thus, for a high value of B, a greater displacement between points 22 and 30 may be tolerated than for a low value of B. Accordingly, hereinafter, squareness ratio will be referred to as the expression V V and the following discussion will consider only values of V and V in the considerations of this squareness ratio.

The excess field condition previously noted is indicated by the displacement between the points 13 and 14 in the hysteresis loop of FIGURE 7. It will be evident that point 13 is the point where saturation first occurs, thus driving the core to point 14 does not give rise to any addition in the residual magnetism remaining at point 16. The advantage is that a greater driving force is used to drive the core to point 14 and this greater driving force provides for a more rapid switching of the core than would be provided if a driving force where employed which was only suflicient to drive the core to point 13. In Chart 1, which follows, there is set forth a listing of compositions of manganese-ferrite systems within the ranges providing square hysteresis characteristics. Four compositions noted as MS, CM, NCM, and K107 are listed and it will be observed that these compositions represent manganese-ferrite systems without and with additive materials. These compositions provide cores over ranges of coercivity extending from 1.1 oersteds to 3.7 oersteds as will be hereinafter described in connection with FIG- URE 1 and having sufiiciently high degrees of squareness to permit switching as has been described in connection with FIGURE 7. Itwill be evident from the listing of the percentages of the constituents of the compositions set forth in Chart 1, that some latitude exists in the exact percentages of the constituents of the compositions.

It has been found, however, that highly square loop manganese-ferrite systems suitable for coincident current operation comprise ranges of Fe O from approximately 38 mol percent to approximately 44 mol percent and ranges of manganese oxide from approximately 51 mol percent to approximately 60 mol percent. It has also been. found that copper oxide may be added up to approximately mol percent, and that chromium oxide and nickel oxide may be added up to approximately a total of 5.11101 percent. The basic concept of this invention will, however, apply to ranges of composition content exceeding those of Chart 1, even though such compositions may not provide the high degree of squareness provided by the compositions of Chart 1.

CHART 1 Compositions in Mal Percent NCM Before proceeding with a detailed description of the invention in conjunction with the drawings, a brief description of the usual techniques employed in the production of magnetic ferrite ferrospinel bodies should be set forth. These techniques involve the mixing of commercially pure fine particles of oxides of desired materials in desired proportions. Such mixing is accomplished, for example, by wet ball milling to form a slurry. The slurry is thereafter dried and the resulting dry cake may be ground to a fine powder. This powder is then placed in a suitable container and calcined in air at temperatures of approximately from 600 C. to 1000" C. for time intervals ranging from 30 minutes to 180 minutes. The actual temperatures and times employed vary with the composi tions involved.

After calcining, the material is again milled and there is added to the material suitable binder and lubricant materials to facilitate the subsequent molding operation. The binder may be polyvinyl alcohol added in the amount of approximately 3% by Weight and the lubricant may be dibutyl p'hthalate added in the amount of approximately 4% by weight.

The resulting mixture is then press molded into the form of the desired body which may be of toroidal or of other desired shape. The body in this condition is 70 termed a green body.

After the molding operation, the green body may be heated to approximately 600 C. and the binder and lubricant which are organic compounds are driven therefrom.

4 sintered at temperatures ranging from approximately 1000 C. to 1500 C. for various time intervals depending upon its compositions and characteristics desired.

The foregoing process steps of mixing, calcining, adding binders and lubricants, molding and sintering are wellknown in the art. However, what has not been heretofore recognized is that for any desired coercivity, maximum squareness can be obtained only by employing the proper values of iron oxide particle size, calcining temperature, pressed density and sintered density, and that the optimum value of each of these variables varies depending upon the particular coercivity desired in the core. Stated other wise, at any coercivity, maximum squareness can be obtained only by employing proper values of these process variables and these values vary over the range of coercivity.

An additional variable not heretofore considered par ticularly pertinent, is the density of the finally sintered core. I have determined that maximum squareness at any coercivity occurs when the sintered density approximates 4.5 grams per cubic centimeter. This knowledge greatly simplifies the determining of optimum values of the process variables for the production of a core of any given coercivity having optimum squareness. In the absence of elaborate equipment sintered density values are much more easily obtained than are electrical values such as those which have been described in connection with FIGURE 7 and in connection with the definition of squareness as represented by the V V ratio employed herein.

In FIGURE 1, there are shown four curves. Curve 31 shows the variation of iron oxide particle size for the production of cores of maximum squareness having various coercivities. Curve 32 shows the variation of calcining temperature for the production of cores of maximum squareness over the range of coercivities. Curve 33 shows the variation of green or pressed density for the production of cores of maximum squareness over the rangeof coercivities. Curve 34 shows the variation of sintering temperature for the production of cores of maximum squareness over the range of coercivities. Curve 35 indicates the linearcondition of sintered density for cores having maximum squareness over the range of coercivities.

Each of the curves of FIGURE 1 is representative of manganese-ferrite systems having ferrospinel square loop characteristics. Each of these curves represents average values of the various data points shown in the drawing for the compositions set forth in Chart 1. Data points are provided for coercivities of 1.1, 1.5, 1.8, 3.4 and 3.7. It will be evident from these curves that each of the variables follows a regular curve over the range of coercivities and that the optimum values for any desired coercivity can be predicted within reasonable limits by the contours of the curves.

, It will be apparent that certain limits are inherent in processes of this type. There are limitations as to the graduations in successive particle sizes that are commercially available. There are purity limitations imposed by commercially available materials. There are various process control variables which enter into all processes such as these. Furthermore, there are limitations and variations in test equipment by which test data is obtained from finished cores. These variations are frequently inherent in electrical measuring apparatus as well as in the conditions of the cores themselves at successive times resulting from temperature, humidity, power supply and other factors which are well known to those experimenting in fields such as this. However, within these limitations inherent to any laboratory process, the data set forth herein is representative and accurate.

7 The particle sizes indicated in FIGURE 1 within the range of approximately 0.6 to 2.0 microns is the average particle size by weight, that is, if a curve is drawn of The molded body is then placed in a furnace and the'particle, size distribution by weight percent, 50%

of the particles are smaller and 50% larger than the average value.

It will be noted from FIGURE 1 that three average particle sizes are employed, these are 0.6, 0.8 and 2.1 microns. These three average particle sizes represent the three steps in particle sizes which are commercially available within these ranges. The 0.6 average particle size material has 90% of the particles by weight within the range of 0.23 micron to 3.0 microns. The 0.8 average particle side has 90% of the particles by weight between 0.29 micron and 2.5 microns. The 2.1 average particle size material has 90% of the particles by Weight between 0.7 micron and 8.6 microns.

From curve 31 of FIGURE 1, it will be evident that the 0.8 particle size falls below the optimum value indicated by the curve 31. The results of this will be noted in connection with the following discussion of the other data points in the figures. It will, however, be evident that the curve shape as drawn in [FIGURE 1 is reliable and that particle size for any desired coercivity can be predicted with reasonable accuracy. It will also be noted that relatively small particle sizes are required for higher coercivity cores whereas larger particle sizes are required for the lower coercivity cores with the particle size rising rapidly as coercivity decreases to 1.1 oersteds.

Curve 32 of FIGURE 1 shows the calcine temperature optimum value at each of the coercivities involved. As noted in the foregoing general discussion of core manufacturing process, calcining times may extend from approximately 30 to 180 minutes. In the examples set forth herein, calcining times were all approximately 90 minutes, this time interval is, however, relatively uncritical. It will be evident, however, that calcining temperature varies substantially linearly with coercivity rising from approximately 750 -C. for 3.7 oersted cores to approximately 950 C. for 1.1 oersted cores.

It will also be noted that the NCM materials for lower coercivities is processed to maximum squareness with calcining temperatures slightly below the temperatures indicated by the curve 32. This results because of the fact that the presence of the copper in the composition reduces the calcining temperature as a result of its effect on the calcining process. These deviations are not excessive and will be appreciated by one skilled in the art.

Curve 33 of FIGURE 1 shows optimum press densities in grams per cubic centimeter tor cores of each of the coercivities. It will be observed that this curve rises substantially linearly from approximately 2.85 grams per cc. for 1.1 coercivity cores to approximately 3.35 grams per cc. for 3.7 coercivity cores and that from the curve optimum press density of cores within the coercivity range can be predicted with reasonable accuracy. 7

Curve 34 of FIGURE 1 indicates the optimum sintering temperature for cores at each of the coercivities and rises from approximately 1100 C. for 3.7 coercivity .cores to approximately 1425 C. for 1.1 coercivity cores. In the lower coercivity ranges, the chrome-nickel materials require slightly higher sintering temperatures and the copper materials require slightly lower sintering temperatures than those indicated by the curve, however, the unique efiects of these additives giving rise to these deviations will be understood by one skilled in the art and the deviations are relatively minor. For all of the examples set forth herein, the sintering time was approximately 10 minutes.

Curve 35 in FIGURE 1 indicates the sintered density accompanying squareness. This density is approximately 4.51 grams per cc. It will be evident that in actual practice, minor variations on either side of this precise figure will occur, thus the range of optimum densities extends trom approximately 4.49 to 4.53. It will be noted that at the 1.5 coercivity, a sintered density of 4.55 is shown for NCM material. This results because of the fact that the iron oxide particle size employed in this material is somewhat smaller than is desirable to produce optimum conditions at 1.5 coercivity. It is believed that if the particle size and sintering temperatures for this material were to be selected as indicated by the curves 31 and 34, the sintered density for the material would fall within the optimum range. However, an outer range of densities is from 4.48 to 4.55.

. FIGURES 2, 3, 4, 5 and 6 show the eifects on squareness, as defined by the V V ratio, of varying any one of the process variables shown in FIGURE 1 and indicate that for maximum squareness the values are substantially those indicated by the curves in FIGURE 1. Also, in each of the curves of FIGURES- 2-6, there is indicated, the value at which the sintered density is within the range 4.48 to 4.55.

In FIGURE 2, each of the curves represents a plot of squareness as expressed by V V versus iron oxide average particle size by Weight in microns taken at data points 0.6, 0.8, and 2.0 microns as has been heretofore discussed in connection with FIGURE 1. Curve 46 is drawn for NCM material at 3.7 coercivity and shows at 47 that maximum squareness is obtained with 0.6 micron particle size. Curve 48 is drawn for NCM material at 3.4 coercivity and shows at 49 that maximum squareness is obtained with 0.6 micron particle size.

Curves 50 and 52 are drawn for NCM and CM materials, respectively, at 1.8 coercivity and show at 51 and- 53, respectively, that maximum squareness is obtained with 0.8 micron particle size.

Curves 54 and 56 are drawn for CM and NCM materials, respectively, at 1.5 coercivity and show at 55 and 57, respectively, that maximum squareness is obtained with 0.8 micron particle size.

Curves 58, 60, 62 and 64 are drawn for M8, K107, NCM and CM materials, respectively, at 1.1 coercivity and show at 59, 61, 63 and 65, respectively, that maximum squareness is obtained with 2.0 micron particle size.

In each of the curves shown in FIGURE 2, the cores of maximum squareness have sintered densities of or most closely approaching 4.51 grams per cc.

In FIGURE 3, each of the curves represents a plot of squareness, as expressed by V V versus calcine temperature in degrees centigrade. Curve is drawn for K107 material at 3.7 coercivity and shows at '71 that maximum squareness is obtained by a calcine temperature of 750 C. Curve 72 is drawn for NCM material at 3.4 coercivity and shows at 73 that maximum squareness is obtained with 75 0 C. calcine temperature.

Curves 74 and 76 are drawn for NCM and K107 materials-respectively, at 1.8 coercivity and show at 75 and 77 respectively, that maximum squareness is obtained with 900 C. calcine temperature.

Curve 78 is drawn for K107 material at 1.1 coercivity and shows at 79 that maximum squareness is obtained with 950 C. calcine temperature. Curve 80 is drawn for NCM material at 1.1 coercivity and shows at 81 that maximum squareness is obtained with 900 C. calcine temperature. As has been previously discussed with respect to NCM materials, higher calcining tends to give a falling off of squareness and thus this material calcines at a slightly lower temperature than would other-wise be anticipated.

In each of the curves shown in FIGURE 3, the cores of maximum squareness have sintered densities of or most closely approaching 4.51 grams per cc.

In FIGURE 4, each of the curves represents a plot of squareness as expressed by V V versus pressed density in grams per cc. Curves 82 and 84 are drawn for NCM and K107 materials, respectively, at 3.7 coercivity and show at 83 and 85, respectively, that maximum squareness is obtained with approximately 3.31 grams per cc. pressed density.

Curve 86 is drawn for NCM material at 3.4 coercivity and shows at 87 that maximum squareness is obtained with approximately 3.1 grams per cc. pressed density.

Curves 88, 90 and 92 are drawn for NCM, K107 and CM materials, respectively, at 1.8 coercivity and show at 89, 91 and 93, respectively, that maximum squareness is obtained with approximately 2.95 grams per cc. pressed density. 1 Curves 94 and 96 are drawn for K107 and NCM materials, respectively, at 1.1 coercivity and show at 95 and 97, respectively, that maximum squareness is obtained with approximately 2.9 and 2.8 grams per cc. pressed density respectively.

In the curves shown in FIGURE 4, the cores of maximum squareness have sintered densities of or most closely approaching 4.51 grams per cc.

In FIGURE 5, each of the curves represents a plot of squareness as expressed by V l V versus sintering temperature in degrees centigrade; The sintering times are approximately minutes. Curves 98 and 100 are drawn for K107 and NCM materials respectively at 3.4 coercivity and show at 99 and 101, respectively, that maximum squareness is obtained with firing temperatures of approximately 1100 C.

Curve 102 is drawn for NCM material at 1.8 coercivity and shows at 103 that maximum squareness is obtained with a sintering temperature of 1280 C.

Curves 104 and 106 are drawn for NCM and CM materials, respectively, at 1.5 coercivity and show at 105 and 107, respectively, that maximum squareness is obtained with a firing temperature of 1310" C.

Curves 108 and 110 are drawn for K107 and NCM materials, respectively, at 1.1 coercivity and show at 109 and 111, respectively, that maximum squareness is obtained with respective firing temperatures of 1430 and 1400 C.

In each of the curves shown in FIGURE 5, the cores of maximum squareness have sintered densities of or most closely approaching 4.51 grams per cc.

In FIGURE 6, each of the curves represents a plot of squareness as express by V V versus sintered density. The squareness ratio variation was accomplished by varying pressed density. All of the other process variables were in accordance with the curves of FIGURE 1. Upon viewing the curves of FIGURE 6, it will be evident that maximum squareness occurs at approximately the value of 4.51 grams per cc. sintered density. Curves 112, and 114 are drawn for NCM and K107 materials, respectively, at 3.7 coercivity and cross the 4.51 sintered density line at points indicated at 113 and 115, respectively.

Curve 116 is drawn for NCM material at 3.4 coercivity and crosses the 4.51 density line at 117.

Curves 120 and 122 are drawn for NCM and K107 materials, respectively, at 1.8 coercivity and cross the 4.51 density line at 121 and 123, respectively. Curve 124 is for CM material at 1.5 coercivity and crosses the 4.51 density line at 125.

Curves 128 and 129 are drawn for NCM and K107 materials, respectively, at 1.1 coercivity and cross the 4.51 density line at 130 and 131, respectively.

While the curves and data points of FIGURE 6 may at first glance appear to be somewhat random, it should be noted that the sintered density scale is highly expanded and the peaking of these curves is clearly in the close vicinity of 4.51 and in all instances within the range of 4.48 to 4.55.

From the foregoing, it will be evident that the invention involves not only the production of manganese-ferrite materials of maximum squareness within specific ranges of coercivities but also the determination of a variable, i.e., sintered density, which can be employed to indicate whether cores of maximum squareness for any given coercivity are being produced.

While the invention has been particularly shown and described with reference to preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1, The process of producing rectangular hysteresis loop 'co ercivity.

ferrite structures of the. manganese ferrite system having enhanced rectangularity of the hysteresis characteristic, said structures having a predetermined coercivity within the limits specified by the axis of abscissas of FIGURE 1, including the steps of:

(a) mixing together powdered material including Fe 0 and a compound of manganese yielding MnO in proportions within the approximate ranges of 38 to 44.4 mol percent Fe o and 51.1 to 60 mol percent MnO, the average particle size of the iron oxide being approximately equal to the value identified by the intersection of curve 31 of FIGURE 1 with an ordinate representing the predetermined coercivity;

(b) calcining the mixture at a temperature approximately equal to the value identified by the intersection of curve 32 of FIGURE 1 with an ordinate representing the predetermined coercivity;

(0) press molding the mixture to a density approximately equal to the value identified by the intersection of curve 33 of FIGURE 1 with an ordinate representing the predetermined coercivity to form a structure; and

(d) sintering said structure at a temperature approximately equal to the value identified by the intersection of curve 34 of FIGURE 1 with an ordinate representing the predetermined coercivity.

2. *In a process of producing a rectangular hysteresis loop ferrite structure of the manganese ferrite system having a predetermined coercivity within the limits specified by the axis of abscissas of FIG. 1, which process includes the steps of mixing together powdered material including Fe O and a compound of manganese yielding MnO in proportions Within the approximate ranges of 38 to 44.4 mol percent Fe O and 51.1 to 60 mol percent MnO, calcining the mixture at a temperature between about 600 C. and about 1000 C., press molding the mixture to a density between about 2.8 to 3.6 grams per cubic centimeter to form a structure, and sintering the structure at a temperature between about 1000 C. and 1500 C., the improvement in said process for obtaining enhanced rectangularity of the hysteresis characteristic of the ferrite structure comprising sintering said structure at a particular temperature approximately equal to the value identified by the intersection of the curve 34 of FIG. 1 with an ordinate representing the said predetermined coercivity.

3. In a process of producing a rectangular hysteresis loop ferrite structure of the manganese ferrite system having a predetermined coercivity within the limits specified by the axis of abscissas of FIG. 1, which process includes the steps of mixing together powdered material including Fe O and a compound of manganese yielding MnO in proportions Within the approximate ranges of 38 to 44.4 mol percent Fe O and 51.1 to 60 mol percent MnO, calcining the mixture at a temperature between about 600 C. and about 1000 C., press moldin-g the mixture to a density between about 2.8 to 3.6 grams per cubic centimeter to form a structure, and sintering the structure at a temperature between about 1000" C. and 1500 C., the improvement in said process 'for obtaining enhanced rectangularity of the hysteresis characteristic of the ferrite structure comprising calcining the mixture at a particular temperature approximately equal to the value identified by the intersection of the curve 32 of FIG. 1 withan ordinate representing the said predetermined 4. In a process of producing a rectangular hysteresis loop ferrite structure of the manganese ferrite system having a predetermined coercivity within the limits specified by the axis of abscissas of FIG. 1, which process includes the steps of mixing together powdered material including Peso and a compound of manganese yielding MnO in proportions within the approximate ranges of 138 to 44.4 mol percent FegO and 51.1 to 60 mol percent MnO, calcining the mixture at a temperature between about 600 C. and about 1000 C., press molding the mixture to a density between about 2.8 to 3.6 grams per cubic centimeter to form a structure, and sintering the structure at a temperature between about 1000 C. and 1500 C., the improvement on said process for obtaining enhanced rectangularity of the hysteresis characteristic of the ferrite structure comprising press molding the mixture to form a structure having a particular density approximately equal to the value identified by the intersection of the curve 33 of FIG. 1 with an ordinate representing the predetermined coercivity.

5. The process of producing rectangular hysteresis loop ferrite structures of the manganese ferrite system, having enhanced rectangularity of the hysteresis characteristic, said structures having a predetermined coercivity within the limits specified by the axis of abscissas of FIG. 1, including the steps of:

(a) mixing together powdered material including Fe O and a compound of manganese yielding MnO in proportions within the approximate ranges of 38 to 44.4 mol percent Fe O and 51.1 to 60 mol percent MnO, the average particle size of the iron oxide being approximately equal to the value identified by the intersection of curve 31 of FIG. 1 with an ordinate representing the predetermined coercivity;

(b) calcining the mixture at a temperature between about 600 C. and 1000 C.;

() press molding the mixture to a density between about 2.8 to 3.6 grams per cubic centimeter to form a structure; and

(d) sintering the structure at a temperature between about 1000 C. and 1500 C. to form a ferrite structure.

6. The process of producing rectangular hysteresis loop ferrite structures of the manganese ferrite system having enhanced rectangularity of the hysteresis characteristic, said structures having a predetermined coercivity within the limits specified by the axis of abscissas of FIG. 1, including the steps of:

(a) mixing together powdered material including Fe O and a compound of manganese yielding MnO in proportions within the approximate ranges of 38 to 44.4 mol percent Fe O and 51.1 to 60 mol percent MnO, the average particle size of the iron oxide being approximately equal to the value identified by the intersection of curve 31 of FIG. 1 with an ordinate representing the predetermined coercivity;

(b) calcining the mixture at a temperature approximately equal to the value identified by the intersection of curve 32 of FIG. 1 with an ordinate representing the predetermined coercivity;

(c) press molding the mixture to a density between about 2.8 to 3.6 grams per cubic centimeter to form a structure; and

(d) sintering the structure at a temperature between about 1000 C. and 1500 C. to form a ferrite structure.

7. The process of producing rectangular hysteresis loop ferrite structures of the manganese ferrite system, having enchanged rectangularity of the hysteresis characteristic, said structures having a predetermined coercivity within the limits specified by the axis of abscissas of FIG. 1, including the steps of:

(a) mixing together powdered material including Fe O and a compound of manganese yielding MnO in proportions within the approximate ranges of 38 to 44.4 mol percent Fe O and 51.1 to 60 mol percent MnO, the average particle size of the iron oxide being approximately equal to the value identified by 10 the intersection of curve 31 of FIG. 1 with an ordinate representing the predetermined coercivity;

(b) calcining the mixture at a temperature between about 600 C. and about 1000 C.;

(c) press molding the mixture to a density between about 2.8 to 3.6 grams per cubic centimeter to form a structure; and

(d) sintering said structure at a temperature approximately equal to the value identified by the intersection of curve 34 of FIG. 1 with an ordinate representing the predetermined coercivity.

8. The process of producing rectangular hysteresis loop ferrite structures of the manganese ferrite system, having enchanced rectangularity of the systeresis characteristic, said structures having a predetermined coercivity within the limits specified by the axis of abscissas of FIG. 1, including the steps of:

(a) mixing together powdered material including F e 0 and a compound of manganese yielding MnO in proportions within the approximate ranges of 38 to 44.4 mol percent Fe O and 51.1 to 60 mol percent MnO, the average particle size of the iron oxide being approximately equal to the value identified by the intersection of curve 31 of FIG. 1 with an ordinate representing the predetermined coercivity;

(b) calcining the mixture at a temperature between about 600 C. and about 1000 C.;

(c) press molding the mixture to a density approximately equal to the value identified by the intersection of curve 33 of FIG. 1 with an ordinate representing the predetermined coercivity to form a structure; and

(d) sinterin the structure at a temperature between about 1000 C. and 1500 C. to form a ferrite structure.

9. The process of producing rectangular hysteresis loop ferrite structures of the manganese ferrite system having enhanced rectangularity of the hysteresis characteristic, said structures having a predetermined coercivity within the limits specified by the axis of abscissas of FIG. 1, including the steps of:

(a) mixing together powdered material including Fe O and a compound of manganese yielding MnO in proportions within the approximate ranges of 38 to 44.4 mol percent Fe O and 51.1 to 60 mol percent MnO, the average particle size of the iron being between about 0.6 and 2.0 microns;

(b) calcining the mixture at a temperature approximately equal to the value identified by the intersection of curve 32 of FIG. 1 with an ordinate representing the predetermined coercivity;

(0) press molding the mixture to a density between about 2.8 and 3.6 grams per cubic centimeter; and

(d) sintering said structure at a temperature approximately equal to the value identified by the intersection of curve 34 of FIG. 1 with an ordinate representing the predetermined coercivity.

References Cited in the file of this patent UNITED STATES PATENTS 2,818,387 Beck et al Dec. 31, 1957 2,905,641 Esveldet et a1 Sept. 22, 1959 FOREIGN PATENTS 532,384 Belgium Apr. 7, 1955 201,673 Australia May 2, 1956 1,125,577 France July 16, 1956 67,809 France Oct. 14, 1957 (Addition) 797,168 Great Britain June 25, 1958 204,795 Austria Aug. 10, 1959 UNETED STATES PATENT OFFICE CERTIFICATE OF CGRRECTION Patent NO 3,054,752 September 189 19 Edgar (j Leaycrait It is hereby certified that error appears in the above numbered patv ent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 56 for "limits" read limitations column 5, line l0, for "side" read sizescolumn 7, line 69, for "embodiment" read embodiments column 9, line 28, after "and" insert about line 63, for "enchanged" read enhanced column 10 line 14, for "enchanced" read enhanced Signed and sealed this 12th day of February 1963.

(SEAL) Attest:

ERNEST w. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. THE PROCESS OF PRODUCING RECTANGULAR HYSTERESIS LOOP FERRITE STRUCTURES OF THE MAGANESE FERRITE SYSTEM HAVING ENHANCED RECTANGULARITY OF THE HYSTERESIS CHARACTERISTIC, SAID STRUCTURES HAVING A PREDETERMINED COERCIVITY WITHIN THE LIMITS SPECIFIED BY THE AXIS OF ABSCISSAS OF FIGURE 1, INCLUDING THE STEPS OF: (A) MIXING TOGETHER POWDERED MATERIAL INCLUDING FE2O3 AND A COMPOUND OF MANGANESE YIELDING MNO IN PROPORTIONS WITHIN THE APPROXIMATE RANGES OF 38 TO 44.4 MOL PERCENT FE2O3 AND 51.1 TO 60 MOL PERCENT MNO, THE AVERRAGE PARTICLE SIZE OF THE IRON OXIDE BEING APROXIMATELY EQUAL TO THE VALUE IDENTIFIED BY THE INTERSECTION CURVE 31 OF FIGURE 1 WITH AN ORDINATE REPRESENTING THE PREDETERMINED CORECIVITY; (B) CALCINING THE MIXTURE AT A TEMPERATURE APPROXIMATELY EQUAL TO THE VALUE INDENTIFIED BY THE INTERSECTION OF CURVE 32 OF FIGURE 1 WITH AN ORDINATE REPRESENTING THE PREDETERMINED COERCIVITY; (C) PRESS MOLDING THE MIXTURE TO ADENSITY APPROXIMATELY EQUAL TO THE VALUE INDENTIFIED BY THE INTERSECTION OF CURVE 33 OF FIGURE 1 WITH AN ORDINATE REPRESENTING THE PREDETERMINED COERCIVITY TO FORM A STRUCTURE; AND (D) SINTERING SAID STRUCTURE AT A TEMPERATURE APPROXIMATELY EQUAL TO THE VALUE INDENTIFIED BY THE INTERSECTION OF CURVE 34 OF FIGURE 1 WITH AN ORDINATE REPRESENTING THE PREDETERMINED COERCIVITY. 